RobRob RR800 build

[Rontone]

Nearly ready to start working on this, just sizing up everything and getting the placement correct, the chassis is almost the same dimensions as a Princeton reverb, same width, a bit taller, but the depth front to back is 1" less so a little more cramped together so I can follow Robs layout and dimensions,

I presume I should have the cap can near the PT and away from the circuit as B+ is on it [but not too close to the PT to keep it getting warm], then the choke nearby that, I presume there's inductance at work in there and its probably a strong field if it has the mains on it,

Then the OT nearest the outputs and Power tubes so as not to run long leads over the B+ area and keep everything a few inches apart

There is an octal socket hole just in the way of everything, if all my tubes are 2.5" spacing the last tube in the line is right next to the octal, but if I space the power tubes 2" apart I can squeeze a little more room and maybe fit the choke or the OT over the octal hole to cover it, maybe leave a little of the hole poking out, to run the wires down,

Or even move the power tubes over a bit, towards the power supply and use an adapter to fit one onto the octal hole and have the OT between the PI tube and Power tubes,hmmmm choices

[Latole]

Fender chassis ; IMO they are very well built amp
Filter caps are in the middle of the chassis

[Latole]

That is what I'll do

[uki]

Follow/copy, known working layouts, misplaced parts may cause, hum, bad hum, even more hum...

[Rontone]

Thanks good sirs,

I'm just having a Friday night in with the cat, done some more work on the cabinet for it, its starting to look like a worn out Marshall now

Just need to find some metal grille for heat vents

[Rontone]

This is a bit more like it, the output tube pair are now 2.25" apart, 2" away from transformers, the yellow tub is the choke position, white tub the OT

The preamp tubes can now spread out a bit to 3" apart, and it leaves space for the wiring to clear nicely underneath the whole way

I could get a blank rear faceplate and move the speaker outputs closer to the OT

Its been a good friday night looking through the scrap pile, found rubber grommets, some carbon resistors with the leads still long, some vintage heatproof sleeving for component legs and some old but still good 1 meg log pots, and a few 1950s chunky Clarostat pots   

[Latole]

".  I could get a blank rear faceplate and move the speaker outputs closer to the OT "
-Rontone


Do you really need to do that ?

[Rontone]

Thats me always overthinking it

I forgot to show the rear panel, the IEC mains socket was just under the back panel, so I was thinking of recutting the chassis to make it look more even,

But then last night I had a go at peeling back the tolex and cutting the wood back, just need to get the corner better with a wood file and re-wrap and glue the tolex nice and square, you can see the whole thing is not very straight,

I may just remake the back panel with some gold grille to give it that 1970's JMP look, or an entire strip of metal back panel like the later 1980s JCM types

[Latole]

Thats me always overthinking it
 

No need to move speaker jack.

You like overthinking !  Use a bigger chassis first

[Rontone]

On the Hammond transformers of this type with removable bell housings, how should I be terminating the unused primary wires and the unneeded secondary bias tap? Inside the housing with an end crimp to cover the end?

Also to double check, the primary has 2x 120v windings I need to join in series for UK voltage, I was going to link the Brown and Black, and use Blue as Live and White as Neutral following the Hammond labelling

[shooter]

bought this at Lowes a couple years back

[Latole]

bought this at Lowes a couple years back

Many model  are easy to find in good hardware store. Home Depot, Lowes..........

[shooter]

Many model  are easy to find

I have a rare version 

[Rontone]

Got grilles!

An order from tube town arrived, awesome, got the OT and choke, pretty much all the parts for the board and other bits and pieces, and enough grille to make a few rear baffles with, maybe a couple of top vents too


I was asking above in post #9 about the Hammond transformers and how to terminate the unused wires properly inside the bell housings and how to link the primaries properly, does anyone have any example pics?

I was thinking either a joining terminal, or solder and heatshrink cover

[acheld]

I would not terminate unused wires inside the bells.  Easier and safer (IMO anyway) to cut any bare wire off of the lead, and then use heat shrink to protect the end.  I just coil any unused leads out of the way next to the transformer.    It's a little messy, but safe and when (not if) I need or want to make changes, it's easy to do so.

I'm sure with some care that terminating inside the bell would be just fine, but why?

[Rontone]

Yeah, that should do fine, there is only the bias tap wire on the secondary, and 100v and 110v on the primary side that need to tuck away somewhere, I will use clips on one of the transformer mounting bolts to hold them in place

And yes making changes in the future, might be wise to keep the bias tap usable.

[PharmRock]

I use those 3M sticky wire-tie pads for tucking unused transformer wires out of the way, or for nice wire routing especially under the board if necessary.  It also negates having to drill a hole or using a mounting bolt for mounting.
they come in various sizes: https://www.amazon.com/dp/B08341K5K1/ref=dp_iou_view_item?ie=UTF8&psc=1

[Latole]

I use those 3M sticky wire-tie pads for tucking unused transformer wires out of the way, or for nice wire routing especially under the board if necessary.  It also negates having to drill a hole or using a mounting bolt for mounting.
they come in various sizes: https://www.amazon.com/dp/B08341K5K1/ref=dp_iou_view_item?ie=UTF8&psc=1

 
Personally, I don't use anything that only holds glue in this type of assembly.
A device made to last for dozens of years requires better built

[sluckey]

I use those 3M sticky wire-tie pads

Telco uses hundreds of those in their cable junction/demarcation boxes. Makes cabling look neat. There are always several that have come loose in airconditioned/humidity controlled buildings. There are a lot more loose ones in outside boxes.

[Latole]

It holds up quite well if the surfaces have been well prepared.

What many people can neglect or do not do well ?

I alway put screw if I use them

[PharmRock]

Got the idea from looking at Dr. Z chassis pics when I was building my JTM45 clone:
https://el34world.com/Forum/index.php?topic=27888.msg306730#msg306730
I don't think he bolts them down, since his chassis all have PEM nuts for mounting sockets, transformers, etc.

I agree that its inevitable that the glue will break down over time....its just a matter of how long.  Maybe using these is a lazy way out of doing a more reliable and permanent connection, but given that my amps will spend 99.99% of their life in a temp and humidity-controlled environment I'm willing to take the risk of the adhesive coming undone.  And if its good enough for Dr. Z, I figure its good enough for my projects. 

[Latole]

Got the idea from looking at Dr. Z chassis pics when I was building my JTM45 clone:
https://el34world.com/Forum/index.php?topic=27888.msg306730#msg306730
I don't think he bolts them down, since his chassis all have PEM nuts for mounting sockets, transformers, etc.

I agree that its inevitable that the glue will break down over time....its just a matter of how long.  Maybe using these is a lazy way out of doing a more reliable and permanent connection, but given that my amps will spend 99.99% of their life in a temp and humidity-controlled environment I'm willing to take the risk of the adhesive coming undone.  And if its good enough for Dr. Z, I figure its good enough for my projects. 

[Rontone]

Had a bit more time to spend on this, more parts arrived, a dry fitting of all the parts and now just need bolts trimming down and shakeproof washers everywhere,

Now the boring bit, it all comes apart again to check for swarf or filings anywhere [especially trapped in the cage nuts, really watch out for that...]

I have cliff jack sockets with plastic body, mono switching type, I notice the high input socket wants a star washer, is that just to ensure a good ground connection when unplugged? I can still hook up the switching parts the same I think

Also cliff sockets on the outputs, I was only using one hooked up anyway as I will not need an aux output, will this also need grounding to chassis separately as the body is plastic also

[PRR]

> I notice the high input socket wants a star washer, is that just to ensure a good ground connection when unplugged?

In some wiring styles, the (either) input jack is THE chassis ground for the entire low-level preamp. So it is important all the time.

Are you asking if Rob's 15 cent washer is excess expense?

[Rontone]

I couldn't quite work out if when unplugged its still grounded, but the switching should work the same, the low input would not be grounded

I think I need to follow the input wiring from the Thor Trinity layout? Is that right

Shielded input cable grounded at the input socket?

[joesatch]

I built the Robinette 800 6v6. used the Princeton chassis and built a cab with a greenback in it. I have some extensive mods on mine, basically all the JEL mods and added diode/transistor clipping 3-way switch also push pull gain and volume pots to engage a v1b cathode bypass cap and or parallel resistor. Depth pot on rear. its a beast of an amp. it's a legit 2204 circuit. i used the layout as per Rob on his site, JJ cap can where he put his

[Rontone]

It took a while getting back to this, managed to put it all together over the Christmas & New Year week, spent some evenings on the cabinet too, found an old Arrow switch, JMP style, just waiting for a badge to complete it and get some valves tested for it and its ready to turn on!

My wiring style is loosely themed on the classic Windows 95 'Pipes' screensaver and David Bowies staircase in Labyrinth 

One thing I didn't think about was the capacitor on the presence pot, what kind of rating is needed in that NFB area, Robs bill of materials quotes a 600v, I have a 100v poly cap in the right value that I put on there, will that do, what would be approximate voltage on the presence pot?

[Ronquest]

That 100V cap should be fine.

[Rontone]

That 100V cap should be fine.

That's great, I think all other parts are about on spec, I raised the preamp bypass cap from 0.68 up to 1uf so hardly a difference, and the NFB is 13k instead of 10k as I had an old type laying around

...I have some extensive mods on mine, basically all the JEL mods and added diode/transistor clipping 3-way switch also push pull gain and volume pots to engage a v1b cathode bypass cap and or parallel resistor...

Yes! I think I will build another one as I have a few more Mullard ECC83's and EF80's to use, and would like to do one hot-rodded, JEL or Jose/Lee Jackson et al mods to spice up the gain, maybe an effects loop and a line out, maybe try and get a real old Greenback for it

Are you asking if Rob's 15 cent washer is excess expense?

Well I am from Yorkshire, 'ats two days wages ere down t'pits, snap for me whippets for a fortneet lad!

[Rontone]

Front badge turned up this morning, ahhhh Rontone, A name you can trust.....  That's why I chose it 

I went for some little crimp on end terminals to finish the unused wires from the mains TX, melted the end insulation a bit, then some heatshrink and a crimp on top

Used a terminal tag to bridge the 6.3v heaters and 6.3v front panel light together, I'm left handed and noticed when putting heater wires on, the way I hold it down then re-twist just before soldering makes my wires pop back up on every leading connection, looks pretty funny zig-zagging around... might use a blob of hot-glue to hold them down,

Just the Fuse, HT and On/Off switch to hook up now and a few small tweaks here and there, the standby switch is a dummy just for show,

[Rontone]

My crazy unnecessary monorail input grid wire...

[Rontone]

I got the valves tested for this and its up and running, sounding really good tone wise,

But I have some input noise when unplugged, with guitar plugged into the Low Input the amp runs great, low background noise and heater hum etc, even at max its great for a high gain amp,

But unplug the lead and your hit with the kind of sound like an ungrounded input, a constant hiss, plug into the High Input and it gets slightly better but still very bad,

Here's a sketch of how I have done the inputs, with cliff switching jacks, plastic bodied so they don't contact the chassis,
I have run the grounding bar from the preamp volume pot all the way through all the input socket ground tabs and to the preamp grounding bus

Not sure if I've created a ground loop here, or a parallel input accidentally? The first gain stage caps are new, resistors new old stock, yet it doesn't sound like a popcorn carbon resistor noise, but maybe a cap leaking DC perhaps?

V1 tested good otherwise so I don't believe its the valve, I really feel its got something to do with the way I have done the grounding bar through the inputs, how could I narrow the problem down further?

[nandrewjackson]

Your input jacks drawing is not the same as Thor post #24.
Post 24 layout had a ground from hi Jack switched ground to low Jack switched tip, that sends the .02 cap from 1st gain stage to ground.


Your drawing isn't providing that cap to ground when using low input.


That could be the noise maker.
Also, is your high input shielded cable grounded on both sides or only 1 side? It's supposed to be only 1 side to ground.


✝️✅🌴💡✝️✅

[Rontone]

Thank You, that's it! I missed the link from the low input to high grounding switch, I confirmed it with a jumper lead and the noise went away, so have just taken out the jack socket and redone the buss bar and wired correctly and its great now 

Its just got hot and humid here, my guitars get up to the right temperature and start to feel like butter, Warm Stratocaster + Mini Marshall + Lynyrd Skynyrd backing tracks = WOOOOT!

...Also, is your high input shielded cable grounded on both sides or only 1 side? It's supposed to be only 1 side to ground....

I have done all grid input shielded wires with the shield grounded at one end only, I will now try going through the amp and maybe add shielded wire to a few other connections and see if it does help with some background noise





I will have a full report and data to post soon, voltages etc and power rating, I took it to a local tech for the tubes testing and get a few refinements to the build

Power tube grid wires were long, tried tight twisting but alas no, still some oscillation, so 47k Grid Stoppers on the power tubes, mounted on the sockets, that helped with some oscillation that was happening, I will investigate further as I think the grid wires can be shortened, or shielded etc,

The oscillation was still there a little, so the NFB resistor was upped in stages, from 10k to 47k, this does affect the Presence control, but still very usable,

A standby switch was inserted after the first Filter Cap but before the choke, and two internal 20mm fuses on each leg of the HT

A 150k bleeder resistor added on the Filter Caps,

Power Tube cathodes are separated and 1 ohm 0.6w resistors added for 'matching' tubes, testing and emergency fusing